The present invention, in some embodiments thereof, relates to medical devices and, more particularly, but not exclusively, to a method and system for ventilation.
In the medical treatment of patients requiring breathing assistance, it is common to insert an endotracheal tube into the trachea of the patient, by way of the mouth, nose or any other surgically created opening. One end of the endotracheal tube is connected to a ventilator which periodically forces air into the lungs through the tube. The inner end of the tube is typically provided with an inflatable cuff which is inflated by conventional means subsequently to the insertion of the tube into the trachea. The inflated cuff is supposed to provide a seal against the interior wall of the trachea.
Ventilation is the process of delivering oxygen to and washing carbon dioxide from the alveoli in the lungs. A patient receiving mechanical ventilation assistance becomes part of a complex interactive system which is expected to provide adequate ventilation and promote gas exchange to aid in the stabilization and recovery of the patient.
Modern ventilators allow the clinician to select and use several modes of inhalation either individually or in combination via the ventilator setting controls that are common to the ventilators. These modes can be defined in three broad categories: spontaneous, assisted or controlled.
During spontaneous ventilation without other modes of ventilation, the patient breathes at his own pace, but other interventions may affect other parameters of ventilation including the tidal volume and the baseline pressure, above ambient, within the system.
In assisted ventilation, the patient “initiates” the inhalation by lowering the baseline pressure by varying degrees, and then the ventilator “assists” the patient by completing the breath by the application of positive pressure.
During controlled ventilation, the patient is unable to breathe spontaneously or initiate a breath, and is therefore dependent on the ventilator for every breath. During spontaneous or assisted ventilation, the patient is required to “work” (to varying degrees) by using the respiratory muscles in order to breath.
The work of breathing performed by a patient to inhale while intubated and attached to the ventilator includes two major components: physiologic work of breathing (the work of breathing of the patient) and work against endotracheal tube imposed resistance.
It is oftentimes desirable to reduce the effort expended by the patient since a high work of breathing load can cause further damage to a weakened patient or be beyond the capacity or capability of small or disabled patients. At an appropriate pressure support ventilation level, the total work of breathing of the patient is shared between the ventilator and the patient. It is desired to know the intra-tracheal pressure so as to set the ventilator properly and relieve the patient's work of breathing.
Traditionally, tracheal pressure is measured by placing a catheter or catheter-tip pressure transducer down the endotracheal tube or by calculating the Intra-tracheal pressure. The pressure loss is estimated from the endotracheal tube diameter, catheter diameter and air flow rate. Typically, data is collected in vitro and used to estimate the pressure loss due to endotracheal tube during clinical use in a patient. The calculated pressure loss is subtracted from the airway pressure to provide the tracheal pressure.
Various techniques for measuring tracheal pressure are disclosed in Wilder et al., Journal of Clinical Monitoring and Computing Vol. 14 No. 1 (1998), 29, and U.S. Pat. Nos. 5,752,921 and 6,450,164. For example, Wilder et al. disclose a technique in which the pressure of an endotracheal tube cuff and air flow through the endotracheal tube during respiration are used for calculating tracheal pressure.
A patient connected to a ventilator requires periodic removal of fluid from the trachea. The present technique as widely practiced in hospitals is to disconnect the ventilator hoses from the patient, and to insert through the tracheal tube a separate, small-diameter suctioning tube which is used to remove the fluids from the trachea. During this periodic process, some temporary breathing assistance is provided, but not of the quality or quantity as provided by the ventilator. This interruption necessarily results in a decrease of the oxygen level of the blood, and for the heart and lungs to have to work harder, a problem for many critically ill patients. Much has been written about the solution to this problem, typical suggestions being to hyperinflate the lungs before and/or after the suctioning process, and varying the parameters of the suctioning operation, including the size of the suctioning tube, the suctioning pressure and its duration.
U.S. Pat. No. 4,351,328, for example, discloses endotracheal suctioning of a patient without interrupting the connection of a patient to a ventilator. An opening is provided in a wall in the fluid conduit between the patient and the ventilator at a location very close to entry into the patient. That opening is sealed in a manner to permit insertion of a suctioning tube therethrough without opening the respiratory supply system to the atmosphere. The person performing the suctioning can vary the depth of insertion of the suctioning tube and control its position.
U.S. Pat. No. 4,574,798, for example, discloses surgical appliance support which accommodates a capped suction catheter opening for allowing deep suctioning of the lungs without disconnecting the patient from the ventilator.
Additional background art includes U.S. Pat. No. 6,227,200, U.S. Pat. No. 4,699,138, U.S. Pat. No. 4,502,482, U.S. Published Application No. 2009/0071484, Frances et al., “Placement of endotracheal and tracheostomy tubes,” Critical Care Nurse, 2004, 24(3):12-14, and Daviskas et al., “Inhalation of hypertonic saline aerosol enhances mucociliary clearance in asthmatic and healthy subjects,” Eur Respir J., 1996, 9:725-732.